Enabling equipment to withstand and control the effects of internal arcing faults

ABSTRACT

Systems and methods for improving control of an internal arc fault in equipment. The equipment includes a bus configured to provide three-phase power from an incoming line. Furthermore, the equipment includes a current loop formed from a first conductor and a second conductor, where current is received from the bus. The current loop uses electromagnetic forces of a short-circuit current caused by an internal arcing fault of the equipment to move the first and second conductors relative to each other. In response to the movement of the first and second conductors, the current loop creates a gap between the first and second conductors where a new arc ignites at the gap. In this manner, the loop design takes advantage of the natural electromagnetic force to reduce the arc energy at the point of initiation and relocates the energy release point to an exhaust vent of the equipment.

TECHNICAL FIELD

The present invention relates generally to electrical power equipment,and more particularly to reducing the fault energy in areas where thepower circuit of the electrical power equipment (e.g., arc-resistantswitchgears, motor control centers or other equipment, such asmedium-voltage motor control centers rated as arc-resistant inaccordance with the Institute of Electrical and Electronics Engineers(IEEE) guide for testing switchgears rated up to 52 kV for internalarcing faults, such as IEEE C37.20.7-207) is accessible through exteriordoors and covers.

BACKGROUND

An arc fault is a high power discharge of electricity between two ormore conductors. Such arc faults may occur internally within electricalpower equipment (also referred to herein as simply “electricalequipment”). These “internal arcing faults” may be said to be abnormalevents that are not addressed by the normal operation of the electricalequipment.

Normal operation involves providing the ability to interrupt and clearshort-circuit events that occur down-stream from the equipment on thecircuit load. When an internal arcing fault occurs in electricalequipment, the electrical equipment requires other devices that arelocated upstream from it to interrupt the short-circuit current. Theupstream device sees the fault as a load side short-circuit and willperform its normal functions to interrupt that short-circuit. To protectpersonnel around the equipment experiencing the fault, a design referredto as “arc-resistant switchgear” was created. This design is intended towithstand and control the effects of the internal arcing fault toprovide time for the upstream protection to operate and clear the fault.Specifically, the arc-resistant switchgear is designed to redirect arcenergy up and out of the equipment, such as via ducts/vents, away fromequipment operators.

Internal arcing events exert large mechanical forces on the mechanicalstructure of the equipment where they occur. This is due, in part, totheir extreme heat (20,000 Kelvin) superheating the surrounding air andalso due to the vaporization of any material the arc energy touches.Such vaporization may result in an expansion of the material, such astransitioning the material from solid to gas. For example, vaporizing acopper bus results in an expansion at a rate of approximately 64,000:1.As a result of such expansion, rapid overpressure and explosion of theequipment is a common occurrence during an arcing fault.

At such high pressure, it is also common for the plasma produced by thearc energy to escape through openings created by the structural failureof the equipment, the openings of covers and doors, or through gapsbetween components of the assembly. Furthermore, the arc energy may alsoroot on the walls of the equipment and erode that material therebycreating holes for the plasma to escape.

Electrical arcs are totally random in both the location where they beginand in the energy they can produce. The arc energy is based on theshort-circuit current level and the arc voltage. The arc voltage iscontrolled by the length of the arc, which can vary dramatically duringan event. Arc-resistant equipment needs to be able to withstand andcontrol these hazardous effects until the upstream protection canoperate.

SUMMARY

In one embodiment of the present disclosure, an equipment witharc-resistant capability comprises a bus configured to providethree-phase power from an incoming line. The equipment further comprisesa current loop formed from a first conductor and a second conductor,where a current is received from the bus. Furthermore, the current loopuses electromagnetic forces of a short-circuit current caused by aninternal arcing fault of the equipment to move the first and secondconductors relative to each other, where the current loop creates a gapbetween the first and second conductors in response to the movement ofthe first and second conductors and where a new arc ignites at the gap.

In another embodiment of the present disclosure, a method for improvingcontrol of an internal arc fault occurring within an equipment comprisesforming a current loop from a first conductor and a second conductor,where the current loop uses electromagnetic forces of a short-circuitcurrent caused by an internal arcing fault of the equipment to move thefirst and second conductors relative to each other. The method furthercomprises creating a gap between the first and second conductors by thecurrent loop in response to the movement of the first and secondconductors, where a new arc ignites at the gap.

The foregoing has outlined rather generally the features and technicaladvantages of one or more embodiments of the present disclosure in orderthat the detailed description of the present disclosure that follows maybe better understood. Additional features and advantages of the presentdisclosure will be described hereinafter which may form the subject ofthe claims of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the present disclosure can be obtained whenthe following detailed description is considered in conjunction with thefollowing drawings, in which:

FIG. 1 illustrates a current loop in accordance with an embodiment ofthe present disclosure;

FIG. 2 is a flowchart of a method for improving the control of aninternal arc fault occurring within an electrical equipment inaccordance with an embodiment of the present disclosure;

FIGS. 3A-3B illustrate a motor control center in accordance with anembodiment of the present disclosure;

FIG. 4 illustrates an enlarged view of a current loop for the motorcontrol center in accordance with an embodiment of the presentdisclosure;

FIG. 5 illustrates the break point of a current loop in accordance withan embodiment of the present disclosure

FIG. 6 illustrates a CLS-24R peak let-through curve in accordance withan embodiment of the present disclosure; and

FIGS. 7A-7D illustrate arc voltage waveforms in accordance with anembodiment of the present disclosure.

DETAILED DESCRIPTION

As stated in the Background section, electrical arcs are totally randomin both the location where they begin and in the energy they canproduce. The arc energy is based on the short-circuit current level andthe arc voltage. The arc voltage is controlled by the length of the arc,which can vary dramatically during an event. Arc-resistant equipmentneeds to be able to withstand and control the hazardous overpressure andhigh-temperature gases created by the arc energy until the upstreamprotection can operate.

The embodiments of the present disclosure provide a means for enablingarc-resistant equipment to withstand and control the effects ofelectrical arcs until the upstream protection can operate.

Referring to the drawings in general, it will be understood that theillustrations are for the purpose of describing particularimplementations of the disclosure and are not intended to be limitingthereto. While most of the terms used herein will be recognizable tothose of ordinary skill in the art, it should be understood that whennot explicitly defined, terms should be interpreted as adopting ameaning presently accepted by those of ordinary skill in the art.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory only,and are not restrictive of the invention, as claimed. In thisapplication, the use of the singular includes the plural, the word “a”or “an” means “at least one,” and the use of “or” means “and/or,” unlessspecifically stated otherwise. Furthermore, the use of the term“including,” as well as other forms, such as “includes” and “included,”is not limiting. Also, terms such as “element” or “component” encompassboth elements or components comprising one unit and elements orcomponents that comprise more than one unit unless specifically statedotherwise.

In one embodiment, the arc fault effects are controlled by controllingwhere the electrical arc moves within the equipment (e.g., arc-resistantswitchgear, motor control center). The high current present during ashort-circuit creates an electromagnetic force that acts on theconductors (e.g., bus bars or cables) causing them to move in a specificdirection defined by the left-hand rule. When current flows through aconducting wire, and an external magnetic field is applied across thatflow, the conducting wire experiences a force perpendicular both to thatfield and to the direction of the current flow (i.e., they are mutuallyperpendicular). According to the left-hand rule, current (I) in thedirection of the middle finger and magnetic flux (Φ) corresponding tothe index finger indicates force (F) in the direction of the thumb.

Electromagnetic force is calculated by:

F=B×I×Conductor Length  (Equation 1)

where F=Force, B=Magnetic Flux Density and I=Current. For single phasecurrent moving in opposite directions, the electromagnetic force iscalculated as follows:

$\begin{matrix}{F = {0.12\frac{I^{2}L}{D}}} & ( {{Equation}2} )\end{matrix}$ whereL = lengthandD = distance

FIG. 1 illustrates a current loop 100 with a length (L) 101 and adistance (D) 102 in accordance with an embodiment of the presentdisclosure. Current (I) 103 moves in the direction shown or clockwisefrom the top of the loop to the bottom, thereby causing force (F) 104 tobe exerted on the top and bottom portions of the current loop inopposite directions. As can be seen from Equation 2, the force increaseswith increasing current (I) and length (L), but decreases withincreasing distance (D).

The same electromagnetic forces that can move the bus during ashort-circuit event can be utilized to separate conductors in the powercircuit and introduce an arc that will: (1) create a series resistiveelement that will reduce the arc energy at the initial fault point, and(2) transfer significant levels of arc energy to a point where thatenergy can be more easily controlled and directed away from wherepersonnel may be working.

In one embodiment, the principles of the present disclosure do notattempt to interrupt current flow or commutate the arcing fault into abolted fault with the design. Instead, the principles of the presentdisclosure take advantage of a phenomenon that naturally occurs during ashort-circuit and use it to reduce the arc energy at the point ofinitiation and relocate the energy release point to an area closer to anexhaust vent for the equipment design.

The equipment enclosure may be designed to withstand, control, anddirect the arc by-products. The current loop design, should it fail toopen, does not impede this activity. The loop provides a consistentfocal point for the arc, regardless of where the initial fault occurswithin the equipment, with little or no additional cost.

Systems and methods discussed herein provide arc-resistance designs tomove an arc and release arc energy to a desired location of theequipment, thereby allowing the equipment to withstand and control theeffects of internal arcing faults. The equipment may be a switchgear, amotor control center (MCC), a medium-voltage MCC, a low-voltage MCC, orthe like. The design introduces a loop of bus bar that will, underconditions of an internal arcing short-circuit of a certain magnitude,use the electromagnetic forces of that short-circuit current to push thebus bars in the loop away from each other, creating a gap between theconductors where a new arc will ignite. The arc, being a resistiveelement, will reduce the fault current level at the original arcinitiation point and cause the arc energy to root itself at the pointwhere the current loop opens at a desired location of the equipment. Indoing so, the energy release becomes consistent and more manageable.This technique also serves to move the hazardous energy of the arcingfault away from undesirable areas and relocates that energy closer to apressure relief venting location. Moving the arc energy away fromundesirable areas, such as the access doors and covers, reduces themechanical stresses on the equipment and helps to minimize the durationof fault gas exposure seen by the equipment, such as the door frameseams. In one embodiment, the current loop is designed to remainconnected during down-stream short-circuit events thereby allowing thecurrent-limiting fuse to clear the fault during normal operation of theequipment.

In one embodiment, a “current loop” is created by forming the bus suchthat the conductor extends from the main bus for a distance and thenreturns via a second conductor to connect with the vertical riser bus inclose proximity to the main bus. Since there is very little impedance inthe conductor, the voltage drop across the loop is very small and thereis no risk of the system voltage breaking down across the loop. As aresult, the gap between the conductors can be very small, where such adistance between the conductors may be used to determine theelectromagnetic forces exerted by the current flow as discussed above.

Systems and methods for providing arc-resistance designs are discussedfurther herein in relation to an MCC, particularly a medium-voltagemotor control center (MVMCC), solely for the purposes of illustration.It shall be understood by one of ordinary skill in the art that variousaspects of the design are applicable to other equipment as well.

MCCs or MVMCCs are assemblies to control some or all electric motors ina central location. A MCC may include multiple enclosed sections havinga common power bus where each section contains a combination starter,which in turn includes a motor starter, fuses or circuit breaker, and apower disconnect. A MCC may also include push buttons, indicator lights,variable-frequency drives, programmable logic controllers, and meteringequipment. MCCs are typically found in large commercial or industrialbuildings where there are many electric motors that need to becontrolled from a central location, such as a mechanical room orelectrical room.

A method for improving the control of an internal arc fault occurringwithin an electrical equipment is discussed below in connection withFIG. 2 .

FIG. 2 is a flowchart of a method 200 for improving the control of aninternal arc fault occurring within an electrical equipment inaccordance with an embodiment of the present disclosure.

Referring to FIG. 2 , in conjunction with FIG. 1 , in step 201, acurrent loop, such as current loop 100, is formed from a first conductorand a second conductor.

In step 202, current, such as from a bus (e.g., a bus configured toprovide three-phase power from an incoming line), is received, where thecurrent flows through current loop 100 from a starting end of the firstconductor towards an opposite end of the first conductor or a connectionpoint electrically connected to the second conductor. Furthermore, thecurrent flows from the connection point or a starting end of the secondconductor towards an opposite end of the second conductor.

In step 203, current loop 100 uses the electromagnetic forces of ashort-circuit caused by an internal arcing fault to move the first andsecond conductors relative to each other.

In step 204, a gap between the first and second conductors is created bythe current loop, such as current loop 100, in response to the movementof the first and second conductors, where a new arc ignites at the gap.

Additional details regarding method 200 is provided below in connectionwith FIGS. 3A-3B, 4-6 and 7A-7D.

Referring now to FIGS. 3A-3B, FIGS. 3A-3B illustrate a nonlimitingexample of a sectioned side view and a rear view of a motor controlcenter 300 (e.g., Powell® MVMCC), respectively, in accordance with anembodiment of the present disclosure.

For the sake of brevity, discussion is limited to relevant portions ofthe MCCs to the systems and methods discussed herein and variouscommonly known components of the MCCs may be present as well. As shownin FIG. 3A, an enclosure 301 is used to house various components of theMCC 300. In one embodiment, as shown in FIG. 3B, MCC 300 includes a mainbus 302 (e.g., a bus configured to provide three-phase power from anincoming line) and a vertical riser bus 303 (e.g., a bus configured todistribute power). The circled area in each view shows the location ofcurrent loop 100 (FIG. 1 ).

FIG. 4 illustrates an enlarged view of current loop portion 100 (FIG. 1) of motor control center 300 (FIG. 3 ) in accordance with an embodimentof the present disclosure. The details shown in FIG. 4 are nonlimitingdimensions and details applicable to examples discussed herein.

In one embodiment, a first conductor or top portion 401 of the currentloop that extends unsupported from a portion of a bus, such as the mainbus, for a desired distance and a second conductor or bottom portion 402of the current loop that connects with another portion of the bus, suchas the vertical riser bus 303, in close proximity to the bus, create a“current loop” 100.

In other words, one end of first conductor 401 is electrically connectedto the main bus 302 or the like, and the opposite end is electricallyconnected to the first end of second conductor 402. In one embodiment,the opposite end of second conductor 402 is electrically connected tothe vertical riser bus 303 or the like. In one embodiment, a portion offirst conductor 401 and second conductor 402 form current loop 100 witha length (L) of the loop and distance (D) between the two conductors orthe top and bottom portions of the current loop. The width and thicknessof the conductors 401, 402 may be any suitable value, but thenonlimiting example shown generally conforms to dimensions of similarcomponents of the bus. In one embodiment, first conductor 401 and secondconductor 402 are secured together for electrical connection via anysuitable fasteners, such as a nut and bolt of a desired size. Similar tothe prior illustration of FIG. 1 , the current (I) 103 flows throughloop 100 in the direction shown by the arrows. In particular, current(I) 103 flows through loop 100 from the start of first conductor 401 viaa bus connection towards connection point 403 with second conductor 402,and from connection point 403 towards the opposite end of secondconductor 402 back to another suitable bus connection. In thenonlimiting example shown, the connection of first conductor 401 to mainbus 302 and the connection of second conductor 402 to vertical riser bus303 are chosen to facilitate a desired current flow direction. In otherembodiments, current loop 100 may be connected to the components of abus in any suitable manner desired that forms a current loop. In someembodiments, at least one current loop is provided for each phase. Inthe example shown, three current loops may be provided for the threephases of the MVMCC equipment (see FIG. 3B). In some embodiments, theequipment down-stream of loop 100 may be protected by a current-limitingfuse.

In the nonlimiting example shown, the length (L) of loop 100 is 4.75inches and the distance (D) is 0.24 inches. The thickness of bothconductors 401, 402 is 0.25 inches and the length of a horizontalportion of second conductor 402 is 7.50 inches. It shall be apparent toone of ordinary skill in the art the dimensions are applicable to theexample shown, but may be modified without undue experimentation forother embodiments with different ratings.

FIG. 5 illustrates the break point of current loop 100 corresponding toFIG. 4 in accordance with an embodiment of the present disclosure. Inone embodiment, current loop 100 is designed to break at the point shownin FIG. 5 when forces caused by the short-circuit current exceed apredetermined level for current loop 100. Similar to the loopspreviously shown in FIGS. 1 and 4 , loop 100 is formed by a firstconductor 401 and second conductor 402. The first and second conductors401, 402 form current loop 100 with length (L) and distance (D) betweenthe two conductors or the top and bottom portions of loop 100. Thevalues for L and D may be selected as desired for the particularapplications in accordance with the discussion provided herein. Thecurrent (I) 103 flows through loop 100 from the start of first conductor401 towards the connection point 403 with second conductor 402, and fromsaid connection point 403 towards the opposite end of second conductor402 (broken arrows). Examples discussed herein involve copper conductors401, 402, but other embodiments may contemplate other conductivematerials.

The connected ends of first and second conductors 401, 402 areelectrically connected and form a connection point secured together witha suitable fastener 501. In one embodiment, fastener 501 allows thefirst and second conductors 401, 402 to be secured together with adesired clamping force at connection point 403. Washers 502 mayoptionally be provided between the surfaces of fastener 501 and firstand second conductors 401, 402. The desired clamping force (N) 503 isinfluenced by the performance desired from current loop 100. Thenonlimiting example shown utilizes a suitable nut and bolt as thefastener 501. The fastener 501 or break point between first and secondconductors 401, 402 needs to hold together at the current levels at andbelow the predetermined limits of a fuse, such as a downstreamcurrent-limiting fuse, so that the fuse can operate to interrupt currentas it is intended for the MCC equipment or the like. It shall beapparent to one of ordinary skill that design factors of current loop100, such as length, distance, clamping force (N), and conductormaterials or friction coefficient (μ), are selected to allow currentloop 100 to remain closed at the current levels of the fuse rating.

It should also be noted that one of the openings in one of conductors401, 402 is significantly larger than the diameter of fastener 501,slotted or the like. The nonlimiting example shown illustrates a slottedopening 504 in second conductor 402, whereas, the other opening 505 infirst conductor 401 is just large enough for fastener 501 to fitthrough. Fault currents beyond the peak let-through interruptingcapability of the fuse are indicative of where the current loopoperation is desirable for an internal arcing fault. In one embodiment,the mating surfaces of current loop 100 provide sufficient frictionalforce to withstand multiple down-stream load faults where the peaklet-through current is reached and not open the loop. A force (F) iscreated by a symmetrical fault current (see Equation 2). When the forceis greater than the frictional clamping force or the force (F_(s)) thedesign factors are selected to handle for the current loop 100 (e.g., 50kA, 60 kA peak let-through), the loop opens due to movement (M) of firstand second conductors 401, 402 in opposite directions (see brokenarrows). In one embodiment, the oversized or slotted opening 504 allowsthe first and second conductors 401, 402 to move relative to each otherwhen the force caused by the current loop exceeds a desired amount ofseparation force (F_(s)). This movement allows the current loop, such ascurrent loop 100, to create a gap between the conductors, such asconductors 401, 402, where a new arc will ignite. In one embodiment, themovement does not shear fastener 501. In one embodiment, such a force isonly on loop 100 until the fuse clears (e.g., maximum of 8.3 ms). Theapplied Force (F_(s)) to separate loop 100 can be determined from thefollowing:

F _(s) =μ×N  (Equation 3)

It shall be apparent to one of ordinary skill in the art that the lengthof current loop 100, the distance between conductors 401, 402 of currentloop 100, the clamping force, and materials (μ, frictional coefficient)are factors relevant and carefully selected so that current loop 100will separate or open at a desired fault current or greater. Thus, theseparation force (F_(s)) at which current loop 100 creates a gap betweenthe conductors, such as conductors 401, 402, where a new arc will ignitecan be tuned in accordance with the above noted factors for differentMCCs, equipment, or the like.

Examples are included to demonstrate particular aspects of the presentdisclosure. It should be appreciated by those of ordinary skill in theart that the methods described in the examples that follow merelyrepresent illustrative embodiments of the disclosure. Those of ordinaryskill in the art should, in light of the present disclosure, appreciatethat many changes can be made in the specific embodiments described andstill obtain a like or similar result without departing from the spiritand scope of the present disclosure.

For purposes of illustration, nonlimiting examples are discussed herein.In particular, a nonlimiting example corresponding to FIGS. 4 and 5 isdiscussed herein. It is noted that prior dimensions and design factorspreviously discussed are not repeated for the sake of brevity. In oneembodiment, the maximum short-circuit current desired for the equipmentis 50 kA rms sym. The peak current for a 50 kA rms sym fault is 130 kAat the crest of the first current cycle. The equipment down-stream ofthe contactor assembly is protected by a current-limiting fuse. Thehighest rated fuse used is a 7CLS-24R which goes into current limitingmode at 42 kA and has a peak let-through current of 60 kA as illustratedin FIG. 6 . FIG. 6 illustrates various peak let-through curves, such asCLS-24R, in accordance with an embodiment of the present disclosure. Asshown in FIG. 6 , the available 50 kA rms (root mean square) currentcorresponds to a 60 kA peak. A 42 kA peak corresponds to an available 16kA rms current.

Using Equation 1 and the dimensions of the nonlimiting example of FIG. 4for a symmetrical fault of 50 kA (60 kA peak let-through):

$F = {0.12\frac{(50)^{2}(4.75)}{0.24}}$ F = 5, 937.5lbs.force

For a symmetrical fault of 16 kA (42 kA peak let-through):

F=608 lbs. force

In one embodiment, a 5/16-18 grade 5 bolt is utilized as a fastener,such as fastener 501 of FIG. 5 , in the nonlimiting example to securefirst and second conductors, such as conductors 401, 402, together.Referring to FIG. 5 , fastener 501 provides a torque equal to 22 ft-lbs.and a clamping force (N) equal to 3,338 lbs. In one embodiment, thefrictional coefficient for a copper-to-copper interface between thefirst and second conductors, such as conductors 401, 402, is μ=1.6.

From the calculations above, the frictional force at the current loopmating surface or connection point 403 is designed to hold 5,937.5 lbs.of force applied to the bar. When the fault current is below theavailable 42 kA rms current, the fuse remains in normal time-currentmelting mode and the maximum sustained forces applied to current loop100 will be less than 608 lbs. for a symmetrical fault of 16 kA, whichis below the force required to overcome the frictional clamping force orseparation force (F_(s)).

When the fault current exceeds 42 kA, the fuse moves into acurrent-limiting mode and will only allow current flow for a maximum ofa ½ cycle (0.0083 s on a 60 Hz system). The current loop design of thepresent disclosure allows the downstream fuse of the equipment, or theMVMCC in this case, to operate in a normal manner. In one embodiment,the force created by the maximum available symmetrical fault current of50 kA (60 kA peak let-through) is 5,937.5 lbs., which is greater thanthe frictional clamping force (e.g., F_(s)≥5,340 lbs.). This force isonly on the loop until the fuse clears (e.g., maximum of 8.3 ms).

Referring now to FIGS. 7A-7D, FIGS. 7A-7D show traces from the arc faulttesting in accordance with an embodiment of the present disclosure. Inparticular, FIG. 7A illustrates the arc voltage for the A-phase (one ofthe three phases of the MVMCC equipment). FIG. 7B illustrates the arcvoltage for the B-phase (one of the three phases of the MVMCCequipment). FIG. 7C illustrates the arc voltage for the C-phase (one ofthe three phases of the MVMCC equipment). FIG. 7D illustrates the arcvoltage for the ground current, where the loop operation of the presentdisclosure reduces the arc energy at the point of initiation andrelocates the energy release point to an area closer to an exhaust ventfor the equipment design.

As shown in FIGS. 7A-7C, there is some indication that the current looprequires around 3 current cycles (50 ms) to open as shown in the arcvoltage waveforms of FIGS. 7A-7C. Therefore, the nonlimiting exemplarycurrent loop should not separate under downstream fault conditionsnormally cleared by the fuse operation below 50 kA.

Systems and methods discussed herein provide arc-resistant equipment ora motor control center (MCC) utilizing a current loop. The current loopmay be formed from two conductors, and the current loop may have alength (L) of parallel conductors of the loop and distance (D) betweenthe two conductors. Current (I) flows through the current loop from thestarting end of a first conductor towards the opposite end or theconnection point electrically connected to a second conductor. Thecurrent flows from the connection point or starting end of the secondconductor towards the opposite end of the second conductor.

In some embodiments, the starting end of the first conductor receivescurrent from the equipment or MCC, such as a bus (e.g., bus 302) of theequipment or MCC, and the opposite end of the second conductor returnscurrent to another portion of the equipment or MCC, such as another bus(e.g., bus 303) of the equipment or MCC. A fastener, such as a nut andbolt, allows the first and second conductors to be secured together witha desired clamping force at the connection point. Due to the currentflow through the current loop, a force may be exerted on the conductorsin opposing directions due to the left-hand rule for magnetic force. Anoversized opening, either in the first or second conductor, allows thefirst and second conductor to move relative to each other when the forcecaused by the current loop exceeds a desired amount of separation force(F_(s)). The movement allows the current loop to create a gap betweenthe two conductors where a new arc will ignite.

In some embodiments, the current loop is designed to create a gap when afault or symmetrical fault exceeds a predetermined amount, such as 50 kAor greater. In some embodiments, the length (L) of the current loop is4.75 inches. In some embodiments, the distance (D) between theconductors of the loop is 0.24 inches. In some embodiments, the frictioncoefficient (μ) of the conductors is μ=1.6. In some embodiments, theconductors are copper. In some embodiments, the clamping force isN=3,338 lbs. In some embodiments, the separation force is 5,937.5 lbs.

Embodiments described herein are included to demonstrate particularaspects of the present disclosure. It should be appreciated by those ofskill in the art that the embodiments described herein merely representexemplary embodiments of the disclosure. Those of ordinary skill in theart should, in light of the present disclosure, appreciate that manychanges can be made in the specific embodiments described, includingvarious combinations of the different elements, components, steps,features, or the like of the embodiments described, and still obtain alike or similar result without departing from the spirit and scope ofthe present disclosure. From the foregoing description, one of ordinaryskill in the art can easily ascertain the essential characteristics ofthis disclosure, and without departing from the spirit and scopethereof, can make various changes and modifications to adapt thedisclosure to various usages and conditions. The embodiments describedhereinabove are meant to be illustrative and should not be taken aslimiting of the scope of the disclosure.

1. An equipment with arc-resistant capability comprising: a busconfigured to provide three-phase power from an incoming line; and acurrent loop formed from a first conductor and a second conductor,wherein a current is received from said bus, wherein said current loopuses electromagnetic forces of a short-circuit current caused by aninternal arcing fault of said equipment to move said first and secondconductors relative to each other, wherein said current loop creates agap between said first and second conductors in response to saidmovement of said first and second conductors, wherein a new arc ignitesat said gap.
 2. The equipment as recited in claim 1, wherein saidcurrent flows through said current loop starting from a starting end ofsaid first conductor towards an opposite end of said first conductor ora connection point electrically connected to said second conductor,wherein said current flows from said connection point or a starting endof said second conductor towards an opposite end of said secondconductor,
 3. The equipment as recited in claim 2 further comprises: asecond bus receiving said current after flowing towards said oppositeend of said second conductor.
 4. The equipment as recited in claim 2further comprises: a fastener securing said first and second conductorsat said connection point.
 5. The equipment as recited in claim 4,wherein said fastener comprises a nut and a bolt.
 6. The equipment asrecited in claim 4 further comprises: an oversized opening either insaid first or said second conductor, wherein said oversized openingallows said first and second conductors to move relative to each otherwhen a force caused by said current loop exceeds a separation force. 7.The equipment as recited in claim 6, wherein said separation forcecorresponds to approximately 5,900 pounds.
 8. The equipment as recitedin claim 1, wherein said gap is created when a fault or a symmetricalfault exceeds a predetermined amount of current.
 9. The equipment asrecited in claim 1, wherein a length of said current loop is 4.75inches.
 10. The equipment as recited in claim 1, wherein a thickness ofsaid first and second conductors is 0.25 inches.
 11. The equipment asrecited in claim 1, wherein a friction coefficient of said first andsecond conductors is 1.6.
 12. The equipment as recited in claim 1,wherein a metal of said first and second conductors comprises copper.13. The equipment as recited in claim 1, wherein said equipmentcorresponds to a motor control center.
 14. The equipment as recited inclaim 1, wherein said equipment corresponds to a switchgear.
 15. Amethod for improving control of an internal arc fault occurring withinan equipment, the method comprising: forming a current loop from a firstconductor and a second conductor, wherein said current loop useselectromagnetic forces of a short-circuit current caused by an internalarcing fault of said equipment to move said first and second conductorsrelative to each other; and creating a gap between said first and secondconductors by said current loop in response to said movement of saidfirst and second conductors, wherein a new arc ignites at said gap. 16.The method as recited in claim 15, wherein said gap is created when afault or a symmetrical fault exceeds a predetermined amount of current.17. The method as recited in claim 15, wherein a metal of said first andsecond conductors comprises copper.
 18. The method as recited in claim15, wherein a friction coefficient of said first and second conductorsis 1.6.
 19. The method as recited in claim 15, wherein said equipmentcorresponds to a motor control center.
 20. The method as recited inclaim 15, wherein said equipment corresponds to a switchgear.